I. Contents The introduction and application of a single-chip dynamic scanning drive digital tube, and gives an example. This lecture will focus on how the microcontroller can decode infrared remote controllers through capture. Through this lecture, the reader can grasp the encoding principle of the infrared remote controller and how to decode the remote controller through the single chip microcomputer. Second, the principle of introduction With the popularity of home appliances and audio-visual products, infrared remote controllers have been widely used in various types of home appliances (such as remote control switches, smart switches, etc.). It has the characteristics of small size, strong anti-interference ability, low power consumption, strong function, low cost, etc. It is also widely used in industrial equipment. In general, a universal infrared remote control system consists of two parts: transmit and receive, as shown in Figure 1: Figure 1 Infrared remote control system block diagram The transmission part mainly includes keyboard matrix, code modulation, and infrared emission control; the receiving part includes conversion of optical and electrical signals, and amplification, demodulation, and decoding circuits. For example, usually the signal emitted by our remote controller for home appliances is to modulate the control command and the system code (a sequence of 0 and 1) corresponding to the corresponding key on a carrier in the range of 32 to 56 kHz, and then the signal is amplified. Drive the infrared emitter to transmit the signal. In addition, the current popular control method is to use an encoder/decoder ASIC chip (refer to SAA3010 infrared encoder chip and HS0038 infrared receiver header mentioned below). Different company's remote control chip, using the remote control code format is not the same. Here, two types that are widely used at present are described. One is the PWM (Pulse Width Modulation) standard of the NEC Protocol, and the other is the PPM (Pulse Position Modulation) standard of the Philips RC-5 Protocol. NEC standard: The frequency of the remote control carrier is 38kHz (duty ratio is 1:3); when a key is pressed, the system first transmits a complete full code, and then a series of short codes are transmitted after the delay until the key is loose. Open stops transmitting. The simple code repetition is a delay of 108ms, that is, the interval between the rising edges of both guide pulses is 108ms. A complete full code is shown in Figure 2. Figure 2 Full code representation under NEC standard Among them, the boot code high 4.5ms, low level 4.5ms; user code 8 bits, data code 8 bits, a total of 32 bits; data 0 can be used "high level 0.56ms + low level 0.56ms" said data 1 It can be expressed as "high level 0.56ms + low level 1.68ms", as shown in Figure 3. A short code can be equated to the sum of the boot code, the inverted bit of system code bit 0, and the end bit (0.56 ms) high time. Fig. 3 Representation of data 0 and 1 under the NEC standard PHILIPS Standard: The carrier frequency is 38kHz; if there is no shortcode, the control code will be switched between 1 and 0 when the key is pressed. If the button is pressed, the control code will not change. A full code can be equivalent to the sum of the start code, control code, system code, and data code, as shown in Figure 4. Figure 4 Full code representation under the PHILIPS standard Data 0 with "low level 0. 889ms + high level 0. 889ms" Said; data 1 with "high level 0. 889ms + low 0. 889ms" (Figure 5). Repeated code repeat delay 114ms. Figure 5 Representation of data 0 and 1 under the PHILIPS standard In this lecture, the SAA3010 infrared remote controller (see Figure 6(a)) is used, which conforms to the RC-5 encoding format of the common PHILIPS standard. Its one-frame code sequence consists of 2 control codes, and 1 bit. Flip code, 5 is the address code, 6 data codes, and the end code. Its data bit length is 1.688ms. The continuous code repetition delay is 108ms, that is, the delay is 108ms and the same frame data is output when each key is pressed. Figure 6 (a) SAA3010 remote control appearance (b) SAA3010 data bits (c) SAA3010 data repetition period As can be seen from Figure 6, the SAA3010's bit transfer method uses dual phase, and the phase of bit 1 and bit 0 is the opposite. In decoding, decoding can be performed in the form of timed sampling. One bit is sampled twice and sampled at one-fourth and three-fourths of the bit waveform respectively. For example, bit 1 is sampled by this method with values ​​0 and 1. . Of course, it is also possible to sample only once, for example, at one-fourth of the waveform, and then resample the period of a waveform so that the value of the bit 1 sample is 0 (this example is used in this example). Third, the circuit detailed As shown in Figure 7 (a), the infrared receiver head decoding circuit is very simple, using an integrated infrared receiver head, integrated infrared receiver head to receive the remote control signal, amplification, detection, shaping in one, and output The TTL signal can be recognized by the microcontroller, which greatly simplifies the complexity of the receiving circuit and the design of the circuit and is convenient to use. In this lecture, the infrared integrated receiver head HS0038 is used, and its appearance is shown in Figure 7(b). It is a black epoxy resin package, free from sunlight, fluorescent light and other light sources interference, magnetic shielding, low power consumption and high sensitivity. In the case of transmitting signals with a low-power transmitting tube, the receiving distance can reach 30m. It is compatible with TTL and COMS circuits. HS0038 is an upright side collector type. It receives the infrared signal at a frequency of 38 kHz and a period of approximately 26 μs. At the same time, it can amplify, detect, and shape the signal to obtain a TTL-level coded signal. Figure 7 (a) Infrared receiver decoding circuit (b) HS0038 appearance The three pins are ground, power supply, and demodulation signal output. In order to respond to the speed, the decoded signal output of the infrared receiving head is connected to the port of the single chip microcomputer P3.3 (external interrupt 1), so that once there is an infrared decoded signal output, the interrupt can be triggered. In addition, the capacitor C7 is used for power supply decoupling filtering to ensure stable operation of the infrared receiver head. Fourth, program design The core program of this lecture design is as follows: Void time0() interrupt 1 (1) Bit in = ~IR_Input; ( 2) TH0 = 0XFF; (3) TL0 = 0X83; (4) IR_Data[IR_sign] = IR_Data[IR_sign] | in; ( 5) IR_count++; ( 6) If(IR_count == 1 || IR_count == 2) (7) { If(in == 0) ( 8) { TR0 = 0; (9) EX1 = 1; (10) Return; ( 11) } } If(IR_count == 3) ( 12) { IR_sign = 1; (13) } Else if(IR_count == 8) ( 14) { If(IR_Data[1] != 0) ( 15) { TR0 = 0; (16) EX1 = 1; Return; } IR_sign = 2; ( 17) } Else if(IR_count == 14) ( 18) { IR_sign = 3; (19) } Else if(IR_sign == 3) ( 20) { TR0 = 0; (21) IR_Success(); ( 22) Return; (23) } Else IR_Data[IR_sign] = IR_Data[IR_sign] 1; (24) Detailed description of the program: (1) Timer interrupt 0 service function, the infrared receiver header decodes the data and triggers the external interrupt 1, triggering a timer interrupt to capture and decode. (2) During decoding, the carrier frequency is changed to low level, that is, the low level is actually 1 and the high level is actually 0. (3) Set the high-order eight-bit initial value of the timer 0, because the set time length is one data bit period. (4) Set the low eight initial value of timer 0. After actual measurement, the bit time of SAA3010 is about 1.655ms. (5) Put infrared data into the lowest position. (6) Infrared count is incremented by one without a timer interrupt. (7) If the current is the 1st and 2nd timer interrupts are entered. (8) If the value of in is 0 at this time, that is if it is found that the first two bits are not all 1s. (9) Turn off timer 0. (10) Open the external interrupt again to receive it. That is, the first two bits must all be 1. (11) Exit to return. (12) If the start bit (2 bits) and the control bit (1 bit) have been received. (13) IR_sign is set to 1, and the received infrared system code is placed in IR_Data[1]. (14) If the current count reaches the eighth time, the 5-bit system code is received. (15) If the received system code is not 0, the system code is required to be all 0. (16) Close the timer and restart the external interrupt and return. (17) IR_sign is set to 2 and the received IR data bits are placed in IR_Data[2]. (18) If the current count reaches the 14th, 6-bit data code is received. (19) IR_sign is set to 3 to indicate that the data code was successfully received. (20) If IR_sign is equal to 3, it means that if the reception is completed. (21) After the reception is completed, timer 0 is turned off and no longer captured. (22) After the completion of the reception, jump to the execution of the IR_Success() function to perform display and reinitialization. (23) Back. (24) Move the data one bit to the left so that the lower bit data is at the lowest bit. V. Debugging points and experimental phenomena Connect the hardware and generate the program by cold start. After the hex file is downloaded to the SCM, open the serial debugging assistant software, set the baud rate to 9600, reset the SCM, and then press the corresponding button on the SAA3010 remote control, you can observe the received data displayed in the receiving window. In addition, the serial communication indicator on the circuit board will flash, P0 will also display the received data on the LED. It is worth noting that different infrared remote control encoding format is different, even if the same model of infrared remote control, the transmitted code value may also be slightly different, for example, the author used the SAA3010 infrared remote control, its position The measured time is about 1.655ms instead of the nominal 1.688ms. Therefore, conditional readers can use oscilloscopes or logic analyzers and other instruments to measure the code values ​​emitted by the remote controller, and the corresponding modifications are captured. The time is guaranteed. In addition, infrared penetrating ability is weak, for example, when we cover the transmitter or receiver head of the remote controller by hand, it is difficult to receive data or introduce interference at this time. Sixth, summary This presentation describes how the 51 microcontroller uses external interrupt triggering and internal timer capture to decode the infrared remote controller. It is briefly summarized as follows: To decode an infrared remote controller, you must first know the encoding standard of the remote controller, whether it is the NEC standard and the PHILIPS standard described in this article, or other encoding formats. Because you do not know the encoding format, it is difficult to judge the encoding and thus cause misinterpretation. code. Secondly, due to the inherent instability of the crystal oscillator (such as remote control and SCM oscillator), in order to ensure the accuracy of decoding, each code should be measured for a long time, such as the use of the instrument or the use of the microcontroller itself, so as to obtain the preparation results.
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